Hydroxylation of cinnamic acids and flavonoids during biosynthesis of anthocyanins in Petunia hybrida Hort.

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Abstract
The effect of hydroxylation genes on the hydroxylation of intermediates of flavonoid biosynthesis in Petunia hybrida is reported. In mutants homozygous recessive, for the gene An9, dihydroflavonols accumulate. The number of hydroxyl groups in the B-ring is determined by the hydroxylation genes Htl and Hfl. A similar effect of Htl and (probably) Hfl occurs in flavanone-accumulating mutants, homozygous recessive for the gene An3. Mutants dominant for Hfl probably accumulate a 5,7,3′,4′,5′-pentahydroxyflavanone. The mutant W43, homozygous recessive for the gene An5, is blocked in an early flavonoid biosynthesis step. It accumulates p-coumaric acid together with caffeic acid. The hydroxylation genes Htl and Hfl, however, are also homozygous recessive, which indicates that the hydroxylation of p-coumaric acid to caffeic acid or derivatives of these compounds is not controlled by Htl. The accumulation of caffeic acid was observed in all mutants investigated so far, regardless of which hydroxylation genes were dominant or recessive. We conclude that hydroxylations involved in anthocyanin biosynthesis occur at the C15 level.